Initially erasable ink composition for a ball point writing instrument

Abstract

An initially erasable ink composition for a ball point writing instrument which ink is characterized by its initial erasability by ordinary pencil erasers when applied by a ball point writing instrument to an absorbent paper-like writing surface and which thereafter develops permanence. The ink composition comprises an elastomer selected from the group consisting of natural rubbers, synthetic rubbers and mixtures thereof, pigment, and a solvent system for said elastomer and pigment. The elastomer is present in the range of about 18-28% by weight of the ink and the pigment is present in the range of about 10-22% by weight of the ink. The solvent system comprises a volatile component present in the range of about 8-30% by weight of the ink and having a boiling point less than about 180° C. and an essentially non-volatile component which is predominantly a low viscosity hydrocarbon oil, essential oil, petroleum derivative, plasticizer or mixtures thereof having a boiling point less than about 300° C. and greater than about 180° C. being present in the range of about 21 to 50.5% by weight of the ink. The solvent system may also include up to 15% by weight of the ink composition of a non-volatile high viscosity material having a boiling point greater than about 300° C.

I claim: 
     
       1. In a ball point writing instrument containing an ink capable of depositing a trace on an absorbent, paper-like writing surface having minute voids therein, said trace being characterized by initial erasability thereof by ordinary pencil erasers and thereafter developing permanence over a period of time; said ink comprising an elastomer selected from the group consisting of natural rubbers, a synthetic rubber which essentially duplicates the chemical structure of natural rubber, and mixtures thereof, pigment, and a solvent system for said elastomer, said elastomer being present in the range of about 18-28% by weight of the ink, said pigment being present in the range of about 10-22% by weight of the ink, said solvent system comprising a volatile component present in the range of about 8-30% by weight of the ink and having a boiling point less than about 180° C. and an essentially non-volatile component being present in the range of about 21-50.5% by weight of the ink and having a boiling point less than about 300° C. and greater than about 180° C. 
     
     
       2. In a ball point writing instrument as defined in claim 1 wherein said ink includes up to 15% by weight of the ink composition of a high viscosity material having a boiling point greater than 300° C. 
     
     
       3. In a ball point writing instrument as defined in claim 1 or 2 wherein said elastomer has a substantially uniform molecular weight distribution over the molecular weight range of about 100,000 to about 900,000. 
     
     
       4. In a ball point writing instrument as defined in claim 1 wherein said essentially non-volatile component has a viscosity within the range of about 1 to about 15 cps. 
     
     
       5. In a ball point writing instrument as defined in claim 2 wherein said high viscosity material has a viscosity of at least about 58 cps. 
     
     
       6. In a ball point writing instrument containing an ink capable of depositing a trace on an absorbent, paper-like writing surface having minute voids therein, said trace being characterized by initial erasability thereof by ordinary pencil erasers and the capability of developing permanence over a period of time, said ink comprising pigment which is present in the range of about 10-22% by weight of the ink, an elastomer, said elastomer being selected from the group consisting of natural rubbers, a synthetic rubber which essentially duplicates the chemical structure of natural rubber, and mixtures thereof, and being present in the range of about 18-28% by weight of the ink, and a solvent system therefor, said solvent system comprising a volatile component present in the range of about 8-30% by weight of the ink and an essentially non-volatile component present in the range of about 21-50.5% by weight of the ink and in which the volatile component has a boiling point less than about 180° C. and said essentially non-volatile component having a viscosity within the range of about 1 to 15 cps and a boiling point less than 300° C. and greater than about 180° C. 
     
     
       7. In a ball point writing instrument as defined in claim 6 wherein said elastomer comprises a mixture of natural rubbers and a synthetic rubber which essentially duplicates the chemical structure of natural rubber, in approximately equal amounts. 
     
     
       8. In a ball point writing instrument as defined in claim 1 or 6 wherein said essentially non-volatile component is a hydrocarbon oil. 
     
     
       9. In a ball point writing instrument containing an ink capable of depositing a trace on an absorbent, paper-like writing surface having minute voids therein, said trace being characterized by initial erasability thereof by ordinary pencil erasers and the capability of developing permanence over a period of time said ink comprising an elastomer selected from the group consisting of natural rubbers, a synthetic rubber which essentially duplicates the chemical structure of natural rubber, and mixtures thereof, said elastomer being present in amount of at least 18% by weight of the ink, pigment which is present in amount of at least 10% by weight of the ink, and a solvent system for said elastomer, said solvent system comprising a volatile component and an essentially non-volatile component, said volatile component having a boiling point less than about 180° C. and being present in an amount of at least 8% by weight of the ink, and said essentially non-volatile component having a boiling point less than 300° C. and above 180° C. and being present in an amount at least 21% by weight of the ink. 
     
     
       10. In a ball point writing instrument as defined in claim 9 wherein said essentially non-volatile component is a low viscosity hydrocarbon oil. 
     
     
       11. In a ball point writing instrument as defined in claim 10 wherein said hydrocarbon oil has a viscosity within the range of about 1 to about 15 cps. 
     
     
       12. In a ball point writing instrument as defined in claim 9 wherein said volatile component is present in the range of about 8-30% by weight of the ink. 
     
     
       13. In a ball point writing instrument as defined in claim 9 wherein said essential non-volatile component is present in the range of about 21 to 50.5% by weight of the ink. 
     
     
       14. In a ball point writing instrument as defined in claim 9 wherein said pigment is present in the range of about 10-22% by weight of the ink. 
     
     
       15. In a ball point writing instrument as defined in claim 9 wherein said elastomer is present in the range of about 18-28% by weight of the ink. 
     
     
       16. In a ball point writing instrument as defined in claim 9 wherein said elastomer has a substantially uniform molecular weight distribution over the molecular weight range of about 100,000 to about 900,000. 
     
     
       17. In a ball point writing instrument as defined in claim 9 wherein said solvent system further comprises up to 15% by weight of the ink composition of a non-volatile high viscosity material having a boiling point greater than 300° C. 
     
     
       18. In a ball point writing instrument as defined in claim 17 wherein said non-volatile high viscosity material has a viscosity of at least about 58 cps. 
     
     
       19. In a ball point writing instrument as defined in claim 9 wherein said elastomer comprises a mixture of natural rubbers and a synthetic rubber which essentially duplicates the chemical structure of natural rubber in approximately equal amounts. 
     
     
       20. In a ball point writing instrument as defined in claim 9 wherein said essentially non-volatile component is a low viscosity essential oil. 
     
     
       21. In a ball point writing instrument as defined in claim 9 wherein said essentially non-volatile component is a low viscosity petroleum derivative. 
     
     
       22. In a ball point writing instrument as defined in claim 9 wherein said essentially non-volatile component is a low viscosity plasticizer.